The present invention relates to a gas purifier apparatus for removing contaminants or impurities from gas streams, and is particularly concerned with an ultra high purity gas purifier for purifying gases to purity levels of at least 1 ppm.
Known gas purifiers typically comprise a cylindrical outer housing or canister having an inlet port at one end for receiving a gas to be purified, and an outlet port at the opposite end for exit of purified gas from the housing. The housing is filled with a suitable gas purification medium and filter through which the gas passes while traveling in a generally axial direction from the inlet port to the outlet port. The purification medium is of any suitable material or materials for removing the contaminants by absorption or the like.
One problem with prior art axial flow gas purifiers is the limitation in purifier capacity for a given flow and purifier volume. Higher gas flow rates require a greater volume of purification media in order to maintain capacity and purification efficiency. Although it is always less costly to increase the length of the purifier housing, rather than it""s diameter, significant length increase will result in lower flow rates for a given pressure drop or unacceptably high pressure drop. Thus, in practice, the only way to accommodate a higher flow rate in an axial flow purifier is to increase the housing diameter. If the inner diameter of the housing is increased to greater than six inches, it becomes an ASME (American Society of Mechanical Engineers) regulated pressure vessel, which must have thicker walls, is more expensive to manufacture, due to regulated requirements, and must have government approval. Thus, there is a need for a gas purifier which permits higher flow rates at the same pressure drop, without increasing diameter.
It is an object of the present invention to provide a new and improved gas purifier apparatus which allows higher flow rates without unacceptable increase in the pressure vessel diameter.
According to one aspect of the present invention, a gas purifier apparatus is provided, which comprises an elongate housing having an internal chamber and a longitudinal axis, an inlet port for entry of a gas to be purified into the chamber, and an outlet port for exit of purified gas from the chamber, a body of purification medium mounted in the chamber, and a barrier assembly in the chamber for guiding gas to flow in a non-axial path through the purification medium while traveling between the inlet port and outlet port.
In one exemplary embodiment, the barrier assembly comprises an inner tubular sleeve and an outer tubular sleeve extending co-axially from one end of the housing, and the body of purification medium is held between the sleeves. The inner and outer sleeves have perforations along at least part of their length for gas flow through the sleeves and purification medium. In one example, the inlet port is connected to the inner sleeve and the outlet port communicates with an annular chamber outside the outer sleeve, with the gas traveling radially outwardly from the inner sleeve to the outer sleeve. Alternatively, the inlet port may communicate with the annular chamber outside the outer sleeve, with the outlet port connected to the inner sleeve, and the gas traveling radially inwardly from the outer sleeve to the inner sleeve and through the purification medium. In another possible arrangement, an inlet port is provided at each end of the housing, communicating with opposite ends of the inner tube, and the outlet port is connected to the outer annular chamber outside the outer sleeve. This arrangement provides better balance in flow through the entire body of purification medium, and will also allow the housing to be longer without unduly impacting flow rate.
In one embodiment of the invention, the inner tubular sleeve and outer tubular sleeve may extend co-axially from the inlet end of the housing, with each sleeve having opposite first and second ends. The first end of the inner sleeve communicates with the inlet port, and the second ends of the sleeves terminate short of the outlet end of the housing. An end wall is provided across the second ends of the sleeves and the purification medium to prevent gas from flowing axially out of the inner sleeve or purification medium.
This arrangement provides a different, non-axial flow path for the gas through the absorption or purification medium, which provides a reduced pressure drop as compared to an equivalent volume of medium with an axial flow path. This will therefore permit higher flow rates to be achieved simply by extending the length of the housing and filter medium, allowing the necessary additional volume of purification medium to be achieved without increasing the housing diameter. Since the gas flow path through the purification medium is radial, increasing the length of the housing does not change the flow path or increase the pressure drop, unless the flow rate is high enough that the internal diameter of the inner tube will lead to constriction. This can therefore avoid the problems and additional expense involved with an axial flow gas purifier having an internal diameter of greater than six inches, although larger diameters may be used for very high flow rates. Even for diameters over six inches, the purifier will still be less costly to manufacture than a purifier of equivalent flow rate with an axial flow direction.
In an exemplary embodiment, the inner filter sleeve has openings of larger size than those in the outer filter sleeve, so that the inner sleeve will filter out larger particulate contaminants while the outer sleeve will perform fine filtration of any remaining particulates. Alternatively, the flow direction may be reversed with the outer filter sleeve having larger openings. The perforations in the inner sleeve end short of the inlet, and the sleeve has an imperforate inlet end portion in this region. This is because the purifier is oriented to vertically. Settling of the purification media will leave a gap containing no media at the upper or inlet end of the housing. By providing no perforations in the inner tube in this region, the risk of gas by-passing the media is avoided. The purifier may alternatively be run vertically upwardly rather than downwardly with the inlet at the lower end. In this case, any remaining particles after the gas passes through the filter medium will tend to settle downwardly under gravity, and not reach the outlet.
The diameter of the inner sleeve may be of the order of 0.75 inches or more, so that flow in the inner sleeve does not introduce any undesirable pressure drop. In one exemplary embodiment, the inner sleeve diameter was 0.75 inches, the outer sleeve had a diameter of the order of 5 to 5.5 inches, and the housing inner diameter was of the order of 6 to 6.5 inches.
The radial flow path of the gas through the purification medium in this invention allows higher gas flow rates to be accommodated with increased purifier medium surface area without unacceptable increase in the pressure drop. Equivalent flow rates to large diameter vessels can therefore be obtained without the expense and disadvantages resulting from a large pressure vessel diameter. This can be scaled up accordingly to vessels several feet in diameter.